The ever increasing need for digital data storage has driven an ever increasing demand for improved magnetic data storage systems, such as magnetic disk drive systems. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected data tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating, but when the disk rotates air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes at least one coil, a write pole and one or more return poles. When current flows through the coil, a resulting magnetic field causes a magnetic flux to flow through the coil, which results in a magnetic write field emitting from the tip of the write pole. This magnetic field is sufficiently strong that it locally magnetizes a portion of the adjacent magnetic media, thereby recording a bit of data. The write field then, travels through a magnetically soft under-layer of the magnetic medium to return to the return pole of the write head.
A magnetoresistive sensor such as a Giant Magnetoresistive (GMR) sensor or a Tunnel Junction Magnetoresistive (TMR) sensor can be employed to read a magnetic signal from the magnetic media. The magnetoresistive sensor has an electrical resistance that changes in response to an external magnetic field. This change in electrical resistance can be detected by processing circuitry in order to read magnetic data from the magnetic media.
The increasing demand for data storage requires an ever increasing need to increase data density. The increase in data density requires ever smaller data bits, which in turn requires ever smaller read and write elements. The increase in data density also requires increasing the magnetic coercivity and anisotropy of the magnetic media in order to ensure the thermal stability of the recorded magnetic signal. These two requirements are at cross purposes, however. The smaller write head produces a smaller magnetic write field, and the increased magnetic media coercivity and anisotropy requires a higher magnetic write field to effectively record to the media.
One way to overcome this conflict and effectively record a signal at very high data density is to employ heat assisted recording, also known as “HAMR” or “TAR”. In a heat assisted magnetic recording system, an optical near field transducer is used to locally heat the magnetic media just at the point of recording. This heating of the magnetic media temporarily lowers the magnetic coercivity, thereby allowing for a magnetic bit to be more easily recorded to the media with a very small magnetic recording head. The media then cools, whereby the magnetic coercivity of the magnetic media again increases making the magnetic signal thermally stable.